The Vertical Profile of Radiative Cooling and Lapse Rate in a Warming Climate

Abstract

The vertical profile of clear-sky radiative cooling places important constraints on the vertical structure of convection and associated clouds. Simple theory using the cooling-to-space approximation is presented to indicate that the cooling rate in the upper troposphere should increase with surface temperature. The theory predicts how the cooling rate depends on lapse rate in an atmosphere where relative humidity remains approximately a fixed function of temperature. This theory is tested with one-dimensional radiative transfer calculations and radiative-convective equilibrium simulations. For climate simulations that produce an approximately moist adiabatic lapse rate, the radiative cooling profile in K/day becomes increasingly top-heavy with increasing surface temperature. If however the temperature profile warms more slowly than a moist adiabatic profile in mid-troposphere then the cooling rate in the upper and lower troposphere increase at more similar rates as the climate warms, with important implications for convection, clouds and associated deep and shallow circulations.